Microscydmus Saulcy & Croissandeau

Jałoszyński, Paweł, 2014, The smallest Cyrtoscydmini of Australia: revision of Microscydmus Saulcy & Croissandeau and Penicillidmus gen. n. (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 3774 (1), pp. 1-30 : 4-5

Microscydmus Saulcy & Croissandeau

Microscydmus Saulcy & Croissandeau, 1893: 225 (without species); type species: Scydmaenus nanus Schaum, 1844 (subsequent monotypy by Croissandeau, 1898: 105).

Morphology and diagnosis of Microscydmus s. str. The nominotypical subgenus of Microscydmus can be defined as a cyrtoscydmine member comprising beetles with typical "ant-like" appearance (i.e., with an elongate body and distinct constrictions between the head and prothorax and between prothorax and pterothorax + abdomen) and extremely small bodies (below 1 mm in length, typically 0.6-0.8 mm), sharing the following combination of characters: i) tempora, genae and sides of pronotum densely covered with straight, long and thick bristles ( Figs. 4 , 8 ); ii) head short, subtriangular or subtrapezoidal ( Figs. 1–2, 4 ) with weakly convex vertex ( Fig. 2 ; vt) and frons slightly projecting anteriorly with its narrow anterior part narrowly separating antennal insertions; iii) antennae with distinct club composed of antennomeres IX–XI; iv) submentum short and broad, without lateral sutures ( Fig. 4 ; smn); v) posterior tentorial pits visible in ventral view and located in distinct transverse groove ( Fig. 4 ; ptp); vi) occipital constriction only slightly narrower than vertex ( Fig. 4 ; occ); vii) prothorax without lateral marginal carinae, with complete hypomeral ridges ( Fig. 8 ; hyr) and basisternal part of prosternum ( Fig. 8 ; bst) laterally fused with internal (adcoxal) part of each hypomeron; viii) pronotum with two pairs of ante-basal pits ( Fig. 9 ; abf), internal pair connected by variously distinct transverse impression or groove ( Fig. 9 ; abg); ix) mesoventrite with asetose impressions and setose impressions ( Figs. 10, 13 ; ai, si) and mesoventral intercoxal process ( Figs. 10, 13 ; msvp) carinate, moderately expanding ventrally and not connected anteriorly to anterior ridge of mesoventrite ( Figs. 10, 13 ; ar); x) metaventral intercoxal process ( Fig. 10 ; mtvp) with two long spines; xi) each elytron with short but distinct and deep basal impression bearing one large basal elytral fovea filled with sparse setae ( Fig. 11 ).

Additionally, species of Microscydmus s. str. are characterized by distinct tempora ( Fig. 4 ; tm); absence of fronto-clypeal groove; antennal insertions located on anterior surface of head; mandibles ( Figs. 2–5 ; md) subtriangular, with indistinct, small and often visible only in ventral view sub-apical tooth ( Fig. 5 ) and large dorsomesal prostheca ( Fig. 3 ; pst); hypostomal ridges ( Fig. 4 ; hr) short and extending postero-mesally, not reaching anterior margin of gular plate; maxillary palpomere III ( Fig. 7 ; mxp3) only 3– 4 x as long as broad, palpomere IV ( Fig. 7 ; mxp4) strongly elongate and slender, with broadened short and setose basal part and distinctly demarcated, abruptly narrowing and nearly rod-like pointed distal part; prementum with short subtriangular or subtrapezoidal ligula ( Figs. 5–6 ; lg) bearing two or three thick setae (in two specimens of M. nanus studied by SEM one has two setae, the other one, illustrated here, three setae; two setae were also found in M. minimus ); prothorax with indistinct, weakly carinate prosternal intercoxal process ( Fig. 8 ; psp); procoxal sockets ( Fig. 8 ) closed by broad lateral projection of coxal part of sternum; pronotosternal sutures ( Fig. 8 ; nss) visible only as short notches in antero-ventral part of prothorax; mesoscutum and mesoscutellum ( Fig. 12 ; sc2+scl2) not separated by scutoscutellar suture, forming single subtriangular plate not visible between elytral bases in intact specimens; aedeagus ( Figs 17–19 ) drop-shaped, with thin walls of median lobe, basally or sub-basally located foramen ( Fig.

17; bo) and free, slender parameres ( Fig. 17 ; pm), typically with single robust apical seta ( Fig. 19 ); spermatheca sclerotized and globular, usually located deeply in thorax.

In at least some species of Microscydmus s. str. and all in the subgenus Parastenichnus Franz, 1970 the protibiae of males have modified apices, bearing externally located combs ( Figs. 14–16 ; ec) composed of several curved teeth fused together at base. Additionally the protibial apex can be armed with another, internally located comb ( Figs. 14–15 ; ic) of several straight cuticular projections, and with two robust ventral spines ( Figs 14–16 ; vs) at base of the tarsomere I. Ventral setae on tarsomeres in the type species of the genus are accompanied by cucticular projections ( Fig. 16 ; cp).

Figures

FIGURES 1 – 4. Morphology of the type species of Microscydmus Saulcy & Croissandeau, M. nanus (Schaum), male. Dorsal habitus (1); head in antero-dorsal view (2); left mandible in dorsal view (3); head in ventral view (4). Abbreviations: bst, basistipes; cd, cardo; cl, clypeus; fr, frons; gal, galea; gp, gular plate; gs, gular suture; hr, hypostomal ridge; lb, labrum; md, mandible; mn, mentum; mst, mesostipes; mxp, maxillary palpus; ppf, palpifer; pst, prostheca; ptp, posterior tentorial pit; smn, submentum; tm, temple; vt, vertex.

FIGURES 8 – 13. Morphology of the type species of Microscydmus Saulcy & Croissandeau, M. nanus (Schaum), male. Prothorax in ventral view (8); base of pronotum in dorsal view (9); pterothorax and abdomen in ventral view (10); base of elytron in dorsal view (11); pterothorax n dorsal view (12); mesothorax in ventral view (13). Abbreviations: abf, ante-basal pronotal fovea; abg, ante-basal pronotal groove; aest 2, mesanepisternum; ai, asetose impression of mesoventrite; alc, alacrista; ar, anterior ridge of mesoventrite; bst, basisternal part of prosternum; hy, hypomeron; hyr, hypomeral ridge; mma, median membranous area; mscc, mesocoxal cavity; mscs, mesocoxal socket; msff, mesofurcal fovea; msp, mesocoxal projection; msvp, mesoventral intercoxal process; mtvp, metaventral intercoxal process; nss, pronotosternal suture; pcc, procoxal cavity; pcs, procoxal socket; pre, prepectus; psn 3, postmetanotum; psp, prosternal intercoxal process; s 3 – 8, abdominal sternites III – VIII; sc 2 + scl 2, mesocutum + mesoscutellum; sc 3, metascutum; si, setose impression of mesoventrite; v 3, metaventrite.

FIGURES 5 – 7. Morphology of the type species of Microscydmus Saulcy & Croissandeau, M. nanus (Schaum), male. Mouthparts in ventral view (5); details of anterior part of labium in ventral view (6); left maxillary palpus in ventral view (7). Abbreviations: gal, galea; lac, lacinia; lg, ligula; lhph, lateral lobe of hypopharynx; lp 1 – 3, labial palpomere I – III; md, mandible; mn, mentum; mst, mesostipes; mxp 1 – 4, maxillary palpomere I – IV.

FIGURES 17 – 19. Morphology of the type species of Microscydmus Saulcy & Croissandeau, M. nanus (Schaum), male. Aedeagus in dorso-lateral view (17); apex of median lobe in dorso-lateral view (18); apex of paramere (19). Abbreviations: aml, apex of median lobe; bo, basal orifice; dw, dorsal wall of median lobe; pm, paramere.

FIGURES 14 – 16. Morphology of the type species of Microscydmus Saulcy & Croissandeau, M. nanus (Schaum), male. Apex of left protibia in ventral view (14); apex of right protibia in internal view (15); apex of left protibia and tarsomere I in ventral view (16). Abbreviations: cp, cuticular projection; ec, external comb; ic, internal comb; trs 1 – 2, tarsomere I – II; vs, ventral spine.